Knowing what is behind you isn't nearly as important and just being predictable in the way you ride your bike. The people behind you don't want to crash into you any more than you don't want them to crash into you.

Though I do want you to use a mirror or consider Varia radar and other brands of radar unit. They aren't going to stop that one crazed driver in a gazillion that intend to harm you. Many accidents cyclist have with motor vehicles are from cyclist doing unexpected things. Whether they were seen behind the cyclist or not. The other part of cycling accidents is when motor vehicles are in front of the cyclist, and the motor vehicle does unexpected things, like turning right or opening the door when parked.

Your issues with getting the rear looking real time camera presentation on a display large enough for you to easily see in the sunlight will be battery life and cost of the equipment to do that. Perhaps in the future, there'll be technology that makes it more viable and practical. But I think it's just a tad too early. Even cars today don't leave their surround cameras on full time. Nor do they attempt to record footage, that many times we wish we'd have when it's time to assess blame for a accident.